Vehicles, for example, truck tractors, may include suspensions that are provided with leveling springs, which may take the form of air bladders. Such suspensions are commonly referred to as air-ride suspensions.
In conventional air-ride truck tractor suspensions mechanical suspension springs, such as leaf springs, may be used to support the sprung mass of the vehicle. In such an arrangement both the mechanical suspension springs and the leveling springs control the ride and handling characteristics of the truck tractor. Air-ride systems are particularly desirable due to the fact that the air springs of the system are connected to a pneumatic air supply on the truck tractor, whereby the amount of air with in the leveling springs may be adjusted in order to vary the height and the ride and handling characteristics of the truck tractor.
For purposes of handling, however, during a roll event, the leveling springs of air ride suspensions tend to only resist roll in the jounce direction as the leveling springs are compressed. The leveling springs on the side of the vehicle that experiences rebound do not generally resist a roll event and in fact encourages roll.
Furthermore, since the mechanical suspension springs support the sprung mass of the vehicle, such suspension springs are normally preloaded in the jounce direction due to the forces exerted by the sprung mass of the vehicle. For this reason, for purposes of handling, during a roll event, the mechanical suspension springs tend to only resist roll in the jounce direction as the mechanical springs are compressed. The mechanical springs on the side of the vehicle that experiences rebound during a roll event will actively encourage roll due to the fact that the springs are preloaded in the jounce direction by the sprung mass of the vehicle.
The present invention relates to a vehicle suspension system that includes leveling springs and mechanical springs, wherein the mechanical springs are provided with a spring rate in a rebound direction that is greater than or substantially equal to a spring rate in a jounce direction and the leveling springs are configured to support the sprung mass at one or more sprung mass load points, whereby the first and second mechanical springs may become substantially unloaded by the sprung mass of the vehicle at one more sprung mass load points.